Reaction of Metal Diethylnitroxides With ‎Pentafluoropyridine, Pentafluorobenzene, ‎Octafluorotoluene and 2-Chloro-3- Or 5-Nitropyridine
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Original research
  • Waheed J. Jondi
  • Adrian J. Adamson
  • Anthony E. Tipping

Treatment of the nitroxides Et2NO M+(2a-c) (M = Na, Li, K) and (Et2NO)2 Ba2+(2d) with pentafluoropyridine (3) at room temperature (1 d) gave in all cases the compounds Py-NEt2(8), Py-ONEt2(9), Py-NHEt (10) and Py-OH2NEt2(11) (where Py = tetrafluoro-4-pyridyl) in the approximate ratio 1:30:30:35. The radical traps, 1,4-dinitrobenzene or galvinoxyl, retarded the reaction (5 d required for complete consumption of 3), but the same products were formed in a similar ratio and compounds 8–11were also formed by decomposition of the amine oxide Py-N+(Ō)Et2(20) [synthesised by the route: 3 + Et2NH → 8 (57%); 8+ (CF3CO)2O/H2O2→20 (81%) as the monohydrate]. It is proposed that the products8–11 arose mainly via an SRNl mechanism involving single electron transfer (SET) from the nitroxide 2 to the substrate 3 leading to the radical anion (21) and hence the tetrafluoro-4-pyridyl radical (22) which reacted with 2 at nitrogen to afford the amine oxide 20. Major Meisenheimer rearrangement of 20 gave hydroxylamine 9, while minor rearrangement afforded the hydroxylamine Py-N(Et)OEt (23) which eliminated ethanal to yield the secondary amine 10. Competing deoxygenation of 20 gave the tertiary amine 8 and the salt 11 [synthesised by reaction of Py-OH (26) with Et2NH] was formed via decomposition of 8 in light (or on heating) involving homolytic fission of the weak N-O bond. Treatment of 9with the acids AHF or CF3SO3H resulted in exothermic reaction and gave compounds 8 (27%, 11%), 10(16%, 18%) and 11 (13%, 25%) via competing protonation at oxygen and nitrogen.

The corresponding reactions of nitroxide 2a with the substrates C6HF5(4) and C6F5CF3(5) afforded the salt 4-H-C6F4-O H2NEt2(12) (15%) and a mixture of the compounds 4-CF3-C6F4-R [R = ONEt2(13)(23%);R = NHEt (14) (2%);R = O H2N+Et2 (15) (12%)], respectively, while treatment of 2a with 2-chloro-3-nitropyridine (6) and 2-chloro-5-nitropyridine (7) gave the tertiary amines 2-N,N-diethylamino-3-nitropyridine (16) (35%) or 2-N,N-diethylamino-5-nitropyridine (18) (25%) together with N-(2-chloro-3-pyridyl)-N-(3-nitro-2-pyridyl)amine (17) (13%) or N-(2-chloro-5-pyridyl)-N-(5-nitro-2-pyridyl)amine (19)(27%) via presumed SRNl pathways.

Journal of Fluorine Chemistry Volume 76, Issue 1, Pages 67–78
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